1. Field of the Invention
The present invention relates to a shelf assembly for firing.
2. Description of the Prior Art
With regard to shelf assemblies for firing ceramic, a shelf assembly has been known that is provided with struts on a kiln car, each of the struts having plural projecting sides for mounting shelf boards and the shelf boards being mounted on the projecting sides (Patent Document 1, for example). Conventionally, in order to stabilize the struts extending in a vertical direction on a kiln car, there have been adopted a method of inserting the tops of struts in an upper plate having strut insertion holes to secure the struts as described in Patent Document 1 and a method of securing the tops of struts 2 supported by a car 3 with tie-beams 4 as shown in FIG. 1.
In these conventional methods, however, the bottoms of struts are immovably secured to the car-top with footing members. When thermal expansion occurs on shelf components during firing processing, a large load is applied especially to the upper ends of struts located in the vicinity of the longitudinal ends to thereby generate a bending stress, and the bending stress causes large distortion on the struts, resulting in warpage or damage of the struts. Conventionally, as a mechanism for relieving such a stress, a margin for accommodating thermal expansion was provided by designing the diameter of holes for inserting bolts to be larger than bolt diameters. However, it was not preferable to design the diameter of holes for inserting bolts to be larger than bolt diameters, because it caused new problems such as vibrations to the shelf assembly.    [Patent Document 1] Japanese Unexamined Patent Publication No. 11-257876